Method for casting metal battery parts



Sept. 18, 1956 H. c. WINKEL 2,763,039

METHOD FOR CASTING METAL. BATTERY PARTS Filed June 23 1955 4 Sheets-Sheet 1 IN VEN TOR.

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Sept. 18, 1956 H. c. WINKEL 2,763,039

METHOD FOR CASTING METAL BATTERY PARTS Filed June 23 1953 4 Sheets-Sheet 5 United States Patent '0 2,763,039 METHOD FOR CASTING METAL BATTERY PARTS Herbert C. Winkel, Watervliet, Mich. Application June 23, 1953, Serial No. 363,600 2 Claims. (CI. 22-57) This invention relates to a method and apparatus for casting metal battery parts, and it is an object of. the

ratus of that character.

The present invention is an improvement over the ap.- paratus disclosed and claimed in Patent No. 2,638,982, issued May 19, 1953, to the present applicant.

In the casting of metal battery parts, and especially of battery grids, considerable difliculty has been encountered in providing a solid casting. Because of the fact that a battery grid casting has a very fine lacy design extending over a substantial enclosed area, it isparticularly diflicult to avoid air pockets or bubbles in the mold cause the desired rapid cooling gives air little opportunlty to escape. The result of air pockets in. the mold is, of course, a discontinuity of the pattern of the castings with resultant mechanical weakness and reduction in current carrying capacity.

It has been found that two important factors in. avoiding this long standing difficulty are accurate temperature control of the poured metal in the mold and the necessity of allowing entrapped air bubbles to rise. to the surface of the poured metal in the mold. The present invention is directed primarily toward the solution of this problem by proper handling of these two closely related factors.

Accordingly, it is another object of the invention to provide an improved method and apparatus for obtaining solid metal battery castings.

It is another object of the invention to provide improved means for maintaining proper temperature of a mold for metal battery castings.

It is another object of the invention to provide an improved n ethod and apparatus for permitting the. escape of en ainped air bubbles to the surface of poured metal in a battery casting mold.

This invention, together with further objects. and.v advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, in which like by like reference numerals,

Fig. l is a perspective view of a battery grid. molding and trimming machine illustrating one embodiment of the invention;

Fig. 2 is a side elevational view of the same machine;

Fig. 3 is a part sectional, part elevational view: of a pump for the molten metal;

Fig. 4 is a side elevational view of the construction shown in Fig. 3;

Fig. 5 is a sectional view showing certain drip catch.- ing apparatus.

Fig. 6 is a plan view of an untrimmed battery grid casting;

parts are designated Fig. 7 is a front view of the stationary half of the grid casting mold;

Fig; 8 is an elevational view of apparatus;

Fig. 9 is an enlarged elevational view, partially broken away, of certain control elements in the cooling apparatus of Fig. 8; and

Fig. 10 is an enlarged view of a portion of the transmission mechanism shown in Fig. 2.

Referring to the drawings in detail, a battery grid moldingand trimming machine is shown which comprises a grid-molding apparatus 1, including a pair of relatively reciprocable molds 2 and 3 separable along a substantially vertical plane, an arcuate slide 4 on which the grid falls when the molds are opened, curved to direct the grid from its vertical position to a substantially horizontal position, a horizontal endless conveyor 5 to which the grid 6 is delivered from the curved slide 4, a grid edge trimmer 7 adjacent the delivery end of the conveyor 5 to which the conveyor, delivers the grid, and a horizontal endless conveyor 8 to which the trimmer 7 delivers thegrid.

The trimmer 7 comprises a pair of stationary trimming edges 9- and 10, one for thefront and one for the rear edge of the grid, and a pair of reciprocating shearing blades 11 and 12 mountedv on a reciprocable head 13, the movable blades 11 and 12 cooperating with the stationary blades, 9 and 10, respectively. The trimmer has a grid-supporting face 14 inclined downwardly and away from the delivery end of the endless conveyor 5, along which face the grid slides to trimming position.

The grids are fed to. the trimmer in timed relation with respect to the operation of the trimmer by a. grid stop plate 15 mounted on leader pins 15bv caused to reciprocated in timed relation to the trimmer head' 13. Whenthe stop plate is in stop position, as shown in dotted lines in Fig.2, it will. be engaged by the lugs 15a cast on the frontedge of the grid" beingfed' forwardly by means of the endless conveyor 5. This will hold the grid against further movement, the. conveyor simply sliding underneath the grid. The stop plate will be held in stop position during a substantial portion of the trimming movement of the trimmer head. When the. trim mer head" is approaching its upper position, the hooks 16 on the trimmer head will engage underneath the stop plate 15 and lift it out. of its obstructing position so that the conveyor 5 can feed the grid forwardly to a position in which it will be delivered and slide onto the inclined grid-supporting face 141 of the trimmer 7.

For'stopping the grid in. correct trimming position an oscillatable stop bar 17 is provided which, in gridlocating positi0n,,is engaged by the pair of forwardly-extending lugs 15a which are cast on the grid. These lugs are at opposite, sides of the grid casting, thus affording widely spaced supports for the grid while being trimmed.

As soon as the. trimmer head has trimmed the edges of the plate and the reciprocable shearing blades 11 and 1 2- have lifted clear of the stationary shearing blades 9 and 10, the further upward movement of the trimmer head will lift the pivoted retaining bar 17 and allow the trimmed grid 6 to fall down onto therguide 18 leading to the endless conveyor 8'. This endless conveyor 8 is driven at such a rate that it will advance about one inch for each plate trimmed and delivered to it. This will cause the plates to be arrangedin a shingle formation on theendless conveyor 8; This shingle-like arrangement facilitates the later handling of the grids as they can be pushed together by taking hold of two widelyseparated grid castings with two-hands and moving them together to cause the plates to slide into astacked formation.

In order to deliver measured quantitiesof moltenmet-al certain mold cooling periodically to the overflow receptacle 13 for the molten metal, pump apparatus 20 (see Figs. 3 and 4) is provided, driven in timed relation to the opening and closing of the grid mold 3 so as to deliver the molten material to the receptacle 119 at a time when the grid mold B is closed. As will be described later, the receptacle is left almost full of molten metal after each discharge stroke of the piston 21. On the next discharge stroke of the piston 21, the molten metal will be delivered to the receptacle 19 and will soon flow over the weir 22 into the flaring entrance 23 to the mold cavity;

In order to prevent accidental slopping over of the receptacle when the grid mold is open, means are provided for withdrawing a small portion of the molten metal from the receptacle during the first part of the charging stroke of the piston 21. For this purpose, the actuating lever 24 for the piston 21 is provided with a laterallyextending arm 25 which engages a collar 26 secured to the discharge valve stem 27 which will prevent the discharge valve 28 from closing against its seat until the piston 21 has moved upwardly on its charging stroke sufliciently to lift the laterally-extending arm 2'5 clear of the valve stem collar 26. During this charging stroke of the piston, some of the molten metal in the overflow receptacle 1-9 will be drawn back into the cylinder 29 through the discharge port 30. The apparatus may be so designed and adjusted that the discharge valve 28 will remain open to enable just the desired amount of molten metal to be withdrawn from the overflow receptacle -19.

The communication between the overflow receptacle 19 and the discharge valve port B is through the pipe 31 leading from the bottom of the overflow receptacle to the chamber 32 underneath the discharge valve port '30. Molten metal is supplied to the chamber 33 above the inlet valve from any suitable source, from whence it flows through the inlet valve port 34 into the cylinder 2-9 when the inlet valve 35 opens. Suitable valve closing springs 36 are provided secured to the upper ends of the valve stems 27 and 37. The high specific gravity of the molten lead also aids in closing the valves.

In order to catch any drip from the overflow weir 22 at a time when the grid molds 2 and B are separated, a drip catcher 38 is provided pivotally mounted at 39 and operated in timed relation to the movement of the grid mold 3 so that when the grid mold is closed and the pump piston 21 is about to start on its discharge stroke, the drip catcher 38 will be moved to the dotted-line position shown, in which it will be out of the way of flow of molten metal over the discharge weir 22. Just before the grid mold begins to separate, the drip catcher 38 will be moved to the full-line position in which it will prevent any molten metal which may slop over the weir 22 from falling down over the face of the open grid mold '2.

The opening and closing of the mold sections 2 and 3, the opening and closing of the drip catcher 38, the operation of the pump 20, horizontal conveyor 5, trimmer 7, and discharge conveyor 8 are all effected from a motordriven shaft '40, rotatable in the direction of the arrow A in Fig. 2.

The movable mold section 3 is reciprocably mounted on a pair of leader pins 41 extending forwardly from the fixed mold section 2. The transmission from the drive shaft '40 to the movable mold section 3 comprises a cam member 410 secured to rotate with the drive shaft 40, a rock lever 42 secured to a rock shaft 43 and having a follower 44 at the end of its downwardly-extending arm for engaging the cam 41a and having alost motion pivotal connection at the upper end of the upwardly-extending arm 42 with a connecting rod 46 secured to the crosshead 47 from which a yoke-shaped operating bar 48 extends into engagement with the notches 49 on the posts 50 secured to the movable mold section. The pivotal and sliding engagement of the upper end of the rock arm 42 with the connecting rod 46 is effected by means of a trunnion block '51 slida'bly mounted on the connecting rod 46 and having its trunnions 52 journalled in the forked end of the rock arm 42. The connecting rod is provided with a shoulder at 53 to limit the sliding movement of the trunnion block 51 on the connecting rod 46. In order to provide some capability for lost motion of the trunnion block on the connecting rod, a coil compression spring 54 is provided surrounding the connecting rod having one end bearing on the trunnion block and the other end bearig on a washer 55 secured to the connecting rod. This lost motion is necessary to enable the desired movement of the drip catcher as described hereinafter.

The transmission from the rotatable shaft 40 to the drip catcher 38 comprises a rock arm 56 secured to rotate with the cam-controlled rock shaft 43, and a connecting rod '57 having a lost motion connection with the upper end of this rock arm and having a pivotal connection 5'8 at its other end with the rockable drip catcher.

As the cam 41a rotates in the direction of the arrow A from a position in which the low portion of the cam is in engagement with the follower 47 to a position in which the high point of the cam is in engagement with the follower, the rock shaft 43 will be rocked clockwise, as seen in Fig. 2, to close the mold. During this closing movement of the mold, the upper end of the rock arm will move from the full-line position shown to the dotted-line position shown in Fig. 5, at which time it is in engagement with the collar '59 on the drip catcher connecting rod 57. The final cam-controlled movement of the rock shaft 43 after the mold cavity has been closed will compress the lost motion spring 5'4 and move the drip catcher connecting rod 57 to the right, as seen in Fig. 2, to move the drip catcher '38 out of the Way of the flow over the discharge weir 22.

This final movement will also bring the pump cam '60 to a position where it will cause the discharge stroke of the pump, forcing molten metal into the receptacle 19 and causing the receptacle to overflow the weir 22 and deliver molten metal to the flaring entrance 23 to the mold cavity in a 'sufficient amount to till the cavity, all of which is described in greater detail below. As the pump-controlling cam 60 moves to a position in which the pump 20 begins its charging stroke, .a relatively small amount of molten metal will be withdrawn from the receptacle 19 back into the pump cylinder 29, the amount withdrawn being sufficient to prevent the receptacle '19 from slopping over due to jarring, or the like, when later on the mold is moved to open position.

The transmission from the rotatable drive shaft 40 to the pump piston rod 21a comprises the cam 60 secured to rotate with the shaft, :1 hell crank lever 61 having a follower 62 on its downwardly-extending arm controlled by the cam 60, a connecting rod 63 pivotally connected at 64 with the other arm of the bell crank lever 61, and the pivotably mounted rock lever 24 having one end se cured at 66 to the upper end of the connecting rod 63 and its other end secured to the upper end of the pump piston rod 21a. The discharge stroke and charging stroke of the pump are effected during a relatively small angular movement of the rotatable shaft by means of the cam plate 60 secured so as to extend beyond the circular dwell portion 67 of the cam. The entire discharge and charging movements of the pump are effected from the time the cam plate 60 first engages the follower at 68 to the time at which the cam plate disengages the follower at 69.

The reciprocable shearing head 13 is mounted on a pair of leader pins 70 extending upwardly from the base of the shearing apparatus. The reciprocable movement of the shearing head from the rotatable shaft 40 is effected by means of a sprocket 71 secured to the rotatable shaft 40, a sprocket chain 72 running over this sprocket 71, a sprocket 73 secured to rotate with the crankshaft 74, a crank arm 75 secured to rotate with this crank-shaft 74, and a connecting rod 76 pivotally secured at. 77 to the crank arm and pivotally connected at 78 with the crosshead OI shea g h d 3 v A similar crank arm and congrasps-s ,necting rod (not shown) may .be provided at the other end of the crosshead.

The horizontal feed conveyor is supported .on a pair of cylinders or drums 79 and 80. The drum 80 is secured to rotate with a shaft 81. This shaft is driven from the shaft 74 by means of a sprocket 82 mounted on the shaft 74, a sprocket chain 83 running over the sprocket 82 and over a sprocket 82a secured to the shaft 81.

The horizontal delivery conveyor 8 is mounted to run over a drum 84 secured to rotate with the shaft 85. This conveyor is driven from the shaft 74 by means of a sprocket 86 secured to rotate with that shaft, a sprocket chain 87 running over this sprocket, and a sprocket 88 over which this chain 87 runs secured to rotate with the shaft 85.

An untrimmed grid 6 is shown in Fig. 6. It is provided with the usual lugs 89 which, when assembled in a battery, form the terminal post for the battery. In casting these battery grids, a flash or fin 90 has invariably been formed, prior to the present invention, on the lower edge of the grid, due to the impracticability of securing sufliciently accurate engagement of the adjacent mold sections at the bottom of the mold. In order to provide a grid casting which will engage properly with the grid-retaining feed bar 15 and the grid-retaining discharge bar 17, there is cast on the advance edge of the grid casting .a pair of positioning lugs 15a by use of the method and apparatus disclosed in application Serial No. 569,715, filed December 26, 1944, now Patent No. 2,467,246, issued to the present applicant. These lugs are cast sufliciently long so as to extend in advance of the most advanced portions of the overflow fin or flash. This enables the 'lugs 15a to engage the positioning bars of the trimming machine to position accurately the grid casting as it is being trimmed. The advance blade trims along the line AB of Fig. 6 to trim off the flash or overflow 90 and lugs 15a and the rear blade trims along the line CD of Fig. 6 to trim oil? the upper edge of the overflow above the line C-D. With the grid thus trimmed, it is a simple matter to break the two grid sections apart by 'hand, the fracture taking place at the two points E and F which are the only points of connection of the trimmed grid sections. As indicated in Figs. 1, 2, and 6, the stop bar 17 is in advance of the shearing plane of the blades 11 and 12 a distance equal to the distance from the trim line A-B to the front edges of the stop lugs 15a.

In order to facilitate the entry of the grid casting into the trimmer, a transversely-extending roller 91 may be mounted between the discharge end of the conveyor and the entrance edge of the trimmer.

In order to lift the locating bar 17 from its grid-holding position, a lifting hook 92 is provided pivotally mounted on the trimmer head 13 at 93 and spring-pressed toward the bar 17 by means of a coil tension spring 94. As the trimmer head moves down, the sloping edge 95 of the book will engage the bar 17 and the hook will slide down past the lower edge of the bar and will then snap into position beneath the bar. After the trimmer head has effected its trimming operation and has moved upwardly sufficiently to disengage the shearing blade from the grid being trimmed, the shoulder 96 on the hook will engage the lower edge of the bar 17 and lift the bar upwardly to release the grid to enable it to slide underneath the bar onto the guide 18 and conveyor 8. As the shearing head 13 continues to move upwardly, the relative paths of movement of the retaining bar 17 and hook 92 will be such that the hook will disengage the bar, allowing it to drop downwardly into position to intercept the advance edge of the succeeding grid delivered to the grid trimmer.

In accordance with the present invention the cam 60 includes two lobes 60a and 60b and an intermediate re cessed portion 600. It will be readily seen that as the cam roller 62 is caused to ride over the cam 60, it will twice be moved outwardly of the circular dwell portion 67 of the cam. Accordingly, the piston 21, see Fig. 3, will twice pump molten metal past the valve 28 into the receptacle 19 and from there into the mold. The size of the cylinder 29 and the length of the stroke of the piston 21 are made to be of such values that the two strokes of the piston caused by .cam lobes 60a and 60b are just sulficient to direct into the mold, the molten metal of the de sired quantity for one casting.

It will be understood that as the cam roller 62 moves from the peak of the first lobe 60a to the point at which it begins to climb the second lobe 6015 no molten metal is being directed into the mold. This period is of sutficient duration to permit the escape of air bubbles from the first poured metal before the second pouring occurs. It is well known to those skilled in the art that air bubbles are frequently trapped in the fine passages of the mold corresponding to the lacy central portion of the individual grids. That is, before the air bubbles can rise to the surface of the poured metal, through these long narrow passages, the metal has chilled to a point that the air bubbles are locked in place. This, of course, results in discontinuity or porosity of the casting, which in turn causes mechanical weakness and reduced electrical contact area of the finished battery grid casting. Some manufacturers deliberately make a loose fit between the edges of the mold halves to permit air to be forced ahead of the incoming metal and out of the bottom of the mold. This is one reason for the common formation of the flashing at the bottom of the battery grids.

According to one feature of the present invention, air bubbles are allowed to escape upwardly through the poured molten metal by virtue of the distinct delay between two separate pourings of molten metal for filling a mold once. It has been found that with the mold only partially filled air bubbles readily reach the surface of the poured metal and escape before the metal freezes.

It will be noted that in the illustrated embodiment a longer stroke of piston 21 is obtained when the cam roller travels substantially radially outward from the dwell 67 to the peak of the lobe 60a (the first pouring action) than when the cam roller 62 rises from the intermediate dwell portion 600 to the peak of the lobe 60b (the second pouring action). This follows from the fact that while the two lobes 60c and 6012 are substantially the same height with respect to the dwell 67, the intermediate dwell 600 is arranged outwardly of the main dwell portion 67. As a result more molten metal is directed into the mold during the first pouring action than in the second and final pouring action.

This particular embodiment of the invention is preferred, since it has been found that air bubbles may readily rise through the molten metal in the mold and escape through the upper surface of the molten metal as long as all of the vertical passages in the mold open directly to the atmosphere. It will readily be seen by reference to Fig. 6 that this is the case after the first pouring action, provided only that the level of molten metal in the mold at that time is below the upper trim line CD. In this condition all of the vertical passages are substantially open to atmosphere in the form of the large horizontal passage lying along the trim line C-D. After the second pouring the entire mold cavity is filled, but a relatively small number of air bubbles need rise through only a relatively short distance through vertical passages to find their way to a point at which they may escape through the pouring gate. Therefore, it will readily be seen that it is preferable to make the first pouring action direct a larger quantity of molten metal into the mold than does the second pouring action.

As indicated above,.it has been found that another important factor in obtaining solid castings is the maintenance of the temperature of the poured metal in the mold at an optimum value. This is accomplished in the illustrated apparatus by maintaining the mold itself at a desired predetermined value, such that the molten metal which is of a given temperature when poured into the mold freezes after an optimum period of time. If the mold is too cold the'metal freezes before it even reaches the bottom of the mold, and certainly before any entrapped air bubbles have had an opportunity to rise to the surface of the molten metal. Conversely, if the mold is too hot there is too long a delay in the freezing of the metal whereby the operation cycle is lengthened and the machine does not produce castings as rapidly as it should. Other difficulties arise when a mold is too hot or too cold, but those mentioned above are the principal difficulties or at least are sufiicient to indicate the desirability of maintaining the mold at an optimum temperature.

Attention is directed to the fact that it is the temperature of the mold with which the present invention is concerned. It is common practice of course to maintain the temperature of the molten metal, before pouring, at a desired value. It is to be assumed that the molten metal supplied to the apparatus disclosed herein is maintained at some desired temperature by apparatus not disclosed in the drawings.

In the illustrated embodiment of the invention, the stationary mold half 2 is cooled by water which passes through drilled holes 101, 102 and 103. These holes may be drilled entirely through the length of the mold half 2 for convenience in manufacture, various openings being plugged as at 104, 105 and 106 to produce a continuous, closed water passage. This passage leads to suitable pipes or conduits 107 and 108, the pipe 107 serving as the water supply and the pipe 108 serving to carry away water which has passed through the passage in the mold.

In Fig. 8 it will be seen that the pipe 107, the water inlet pipe, leads to apparatus 109 which may be any suitable form of automatically controllable valve such as that illustrated in Fig. 9. In that figure it will be seen that water enters from below and passes through a drilled hole 110 to encounter a valve 111. When the valve 111 is closed the water may progress no further. However, when the valve 111 is raised the water may pass through gates 112 to enter an annular chamber 113 from which it may pass into the pipe 107.

The valve 111 is operated by control apparatus 115 which in turn is responsive to a thermostat 116 which is shown in Fig. 7 arranged in a drilled hole 117 in the mold half 2. Since many forms of such control apparatus are known in the art and since the particular form of this apparatus does not constitute a feature of the present invention, it is not further described herein. It is believed to be sufficient for the purpose of the present application to point out that it may be responsive to either a pressure signal or an electrical signal, and when one signal is received the valve 111 is caused to close, whereas reception of a different signal causes the valve 111 to open and permit the passage of cooling water therethrough.

Referring again to Figs. 7 and 8, a suitable connection 118 is provided between the thermostat 116 and the control apparatus 115. The thermostat 116 may also be of any suitable form, many of which are well known in the art, and accordingly is not described in detail herein. It is sutficient for the purpose of the present application to point out that the thermostat 116 preferably provides either a pressure signal or an electrical signal which is transmitted along the connection 118 to the control apparatus 115. When the temperature of the mold, i. e., the temperature of the thermostat 116, exceeds some optimum value, a signal is sent along the connection 118 to the control apparatus 115 which, in turn, opens the valve 111 to permit the passage of a larger quantity of cooling water. Conversely, when the temperature of the mold half 2, i. e., the temperature of the thermostat 116 falls below that optimum value, a signal is sent along 8 the connection 118 to the control apparatus to cause the valve 111 to reduce the flow of cooling water.

It is to be noted that the water passage in the mold half 2, namely, the drilled holes 101, 102 and 103' are independent of the mold cavity 120. Also, in accordance with the'preferred embodiment of the invention, the drilled hole 117 for the thermostat 116 is independent of both the mold cavity and the passage for the cooling water.

It will now be seen that the two principal features of the present invention are very closely related in that both serve in cooperation to permit the formation of solid grid castings rapidly. More specifically, the above described apparatus facilitates the escape of air bubbles from the poured molten metal in the mold by maintaining the mold at such a temperature that a reasonable period of time is allowed for the escape of air bubbles before the metal freezes, and by partially filling the mold with molten metal and then allowing a short period of time for the escape of air bubbles from the poured metal before the mold is completely filled by the pouring of additional molten metal. Either of the two principal features of the invention can be only partially successful in obtaining solid castings without the presence of the other.

Attention has already been directed to the fact that the thermostat 1-16 and the cooperating control apparatus 115 may be of any suitable form. It should be further noted that the thermostat 116 might be arranged in the movable mold half 3, although the illustrated embodiment is preferred. Suitable temperatures to be maintained by the thermostatic apparatus have not been suggested since the optimum temperature depends upon many factors, including the size of the mold, the size. of the mold cavity, the material of which the mold is constructed, the distance between the thermostat and the mold cavity, the particular metal employed for the cast:- ings, and the temperature of the molten metal as poured. Various other factors enter into the determination of a suitable temperature setting for the thermostatic apparatus, and since anyone skilled inthe art can readily determine from experience the desired temperature setting, no specific figure is suggested herein.

Similarly, the cam 60, which controls the pouring of the metal, may be of various configurations whereby it may control the rapidity of pouring, the amount poured, the number of pourings to completely fill the mold, and the period of time between the successive pourings re quired to completely fill the mold. Obviously, various forms of electrical or mechanical apparatus may be employed in place of the cam 60 and associated apparatus.

The particular embodiment of the invention described above is one particularly designed for casting battery grid castings. As previously indicated, the invention is also adapted to casting other metal battery grid parts, such as posts and connectors. It has been found that such parts are markedly more solid (having fewer air pockets 'or bubbles) where the present invention is applied to their casting. This is particularly true where both features of the invention are applied in cooperation. 1

It has also been found that where the present invention is employed, metal battery parts may be cast with less flashing, such as the fin 90 of Fig. 6. This advantage is also best obtained by employment of both features of the invention in cooperation. The escape of air from the poured metal, as permitted by the invention, permits use of a tight mold. Also, the maintenance of proper mold temperature causes less warping and other distortion of the mold whereby tightly fitting mold halves become possible.

While one particular embodiment of the invention has been shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall Within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

l. The method of making battery grid castings which comprises directing a quantity of molten metal into a mold, said quantity being insuflicient to fill said mold, interrupting the direction of molten metal into said mold, for a sufiicient time to submit air bubbles entrapped below the surface of the molten metal in said mold to escape through said surface, and then immediately directing another quantity of molten metal into said mold, said quantities of molten metal in total being suflicient to fill said mold.

2. The method of claim 1 in which the quantity of molten metal first directed into said mold is substantially larger than the second quantity of molten metal directed into said mold.

References Cited in the file of this patent UNITED STATES PATENTS 

